Data carrier with sensor

ABSTRACT

In a circuit for a data carrier, which data carrier comprise a sensor that is designed for providing a sensor signal that represents an environment parameter and a communication element that is designed for the contact-less communication with an interrogator station, first connection elements for connecting the circuit to the communication element and second connection elements for establishing an electronic connection of the circuit to the sensor are provided, wherein the second connection elements are realized by the first connection elements and wherein the circuit comprises a sensor signal processing stage designed for receiving said sensor signal via the first connection element and for processing said received sensor signal.

RELATED PATENT DOCUMENTS

This patent document is a continuation under 35 U.S.C. §120 of U.S.patent application Ser. No. 12/094,308 filed on May 20, 2008 (U.S. Pat.No. 8,143,999), which is a 35 U.S.C. §371 national stage entry ofInternational Application No. PCT/IB2006/054404 filed on Nov. 23, 2006,which claims priority benefit under 35 U.S.C. §119 of European PatentApplication No. 05111251.4 filed on Nov. 24, 2005, to which priority isalso claimed here.

FIELD OF THE INVENTION

The invention relates to a circuit for a data carrier, which circuit isdesigned for communicating with a read and/or write station.

The invention further relates to a data carrier comprising a circuitaccording to the preceding paragraph and sensor means.

The invention further relates to a system for communicating measurementdata, which system comprises a data carrier according to the precedingparagraph and a read and/or write station.

The invention further relates to a method of interrogating a sensorsignal from sensor means in a data carrier, which data carrier comprisesa circuit according to the first paragraph and sensor means.

The invention further relates to a sensor for use in a data carrieraccording to the second paragraph.

BACKGROUND OF THE INVENTION

A system for communicating measurement data that performs a method ofinterrogating measurement signals from sensor means in a data carrier isknown from the document EP0563713. The known system comprises aread/write station and at least one data carrier of the contactlesstype. The data carrier comprises an integrated circuit for logicoperations and signal processing and a communication coil arrangementthat is connected to the circuit. The communication coil arrangement isdesigned for the inductive coupling with a corresponding communicationcoil arrangement of the read/write station such that the circuit in thedata carrier can be electrically powered and operated by means of aradio frequency signal that is generated and transmitted by theread/write station. The data carrier further comprises sensor means thatare designed for sensing an environment parameter and for providing asensor signal that represents the sensed environment parameter. In theprior art data carrier, the communication coil arrangement is connectedto the circuit via antenna-connection pads. The sensor means areconnected to the circuit via sensor-connection means that are differentfrom the antenna-connection pads. The sensor means are powered via thecircuit. In operation the known read/write station generates said radiofrequency (RF) carrier signal that powers said data carrier andtransmits a sensor data interrogation command to the data carrier. Thecircuit of the data carrier detects this command and interrogates saidsensor signal from the sensor means and returns measurement datarepresenting the sensor signal via the RF signal.

The known system suffers from the problem that sensor means must beeither integrated with the circuit in order to utilize asemiconductor-based interface with the circuit, which integration isobviously relatively expensive and takes much semiconductor space, orthe sensor means must be connected via additional connection pads to thecircuit in the case of utilizing a conventional sensor locatedexternally with regard to the circuit.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a circuit of the typementioned in the first paragraph and a data carrier of the typementioned in the second paragraph and a system of the type mentioned inthe third paragraph and a method of the type mentioned in the fourthparagraph which obviate the drawbacks described above.

To achieve the object described above, characteristic features accordingto the invention are provided with a circuit according to the invention,so that a circuit according to the invention can be characterized asfollows:

Circuit for a data carrier, which data carrier comprises sensor meansthat are designed for providing a sensor signal that represents anenvironment parameter and communication means that are designed forcontactless communication with an interrogator station, said circuitcomprising first connection means for connecting the circuit to thecommunication means and second connection means for establishing anelectronic connection of the circuit with the sensor means, wherein thesecond connection means are realized by the first connection means, andwherein the circuit comprises sensor signal processing means designedfor receiving said sensor signal via the first connection means and forprocessing said received sensor signal.

To achieve the object defined above, a data carrier according to theinvention comprises a circuit according to the invention.

To achieve the object defined above, a system according to the inventioncomprises a read and/or write station and at least one data carrieraccording to the invention.

To achieve the object defined above, characteristic features accordingto the invention are provided with a method according to the invention,so that a method according to the invention can be characterized asfollows:

Method of interrogating a sensor signal from sensor means in a datacarrier, which data carrier is designed according the invention, whichmethod comprises a step of receiving the sensor signal via firstconnection means of the circuit of the data carrier, which connectionmeans are connected to communication means of the data carrier andestablish an electronic connection between the circuit and the sensor.

To achieve the object described above, characteristic features accordingto the invention are provided with a sensor according to the invention,so that a sensor according to the invention can be characterized asfollows:

In an example embodiment there is a circuit for a data carrier, whichdata carrier comprises sensor means for providing a sensor signal thatrepresents an environment parameter and communication means forcontactless communication with an interrogator station. The circuitcomprises a first connection means for connecting the circuit to thecommunication means for communicating with the interrogator station, andfor receiving radio frequency power from the interrogator station. Thereis a second connection means for establishing an electronic connectionof the circuit to the sensor means, wherein the second connection meansare realized by the first connection means and a sensor signalprocessing means for receiving said sensor signal via the firstconnection means, for processing said received sensor signal, and forproviding an output based upon the received sensor signal, to theinterrogator station via the first connection means. A first connectionpad and a second connection pad constitute the first connection means,the respective pads coupling the circuit for simultaneouslycommunicating with both the communication means and the sensor means. Acircuit configured and arranged to short-circuit radio frequency signalsis coupled to the connection pads from the communication means, during asensing period in which the signal processing means is receiving asignal from the sensor means, via the respective pads.

The provision of the characteristic features according to the inventioncreate the advantage that a sensor can be connected to the circuit ofthe data carrier in a relatively simple manner by using the firstcommunication means of the circuit both for the purpose of exchangingdata with the read/write station and for the purpose of interrogatingthe sensor signal from the sensor. This in addition provides theadvantage that no semiconductor-based interface needs to be providedwithin the circuit and no dedicated additional connecting means arerequired in the circuit for facilitating a connection of the sensor tothe circuit. In particular, existing and well proven standard sensors,which are relatively inexpensive and are either of the-self powered ornon-self-powered type, can be incorporated and used within the datacarrier in a reliable and efficient way, which will accelerate thecommercial market penetration of sensor-equipped radio-frequencyidentification devices for e.g. logistics, safety applications, and/orgoods-monitoring purposes. In a preferred embodiment of the invention,the sensor according to the invention will be used in a data carrieraccording to the invention, because it provides the advantage that thesupporting power source of the sensor will only be utilized when an RFfield is received via the communication means of the data carrier. Thiswill significantly prolong the operational life of the supporting powersupply of the sensor, because the supporting power supply will only beutilized if there is a certain probability that the sensor signal willbe interrogated, which in fact will only take place upon receiving ofthe RF field which provides electrical power for the operation of thecircuit of the data carrier.

Some solutions of the invention provide connectors for connecting thecommunication means of the data carrier to the circuit of the datacarrier. In a preferred solution, however, the circuit comprisesconnection pads for allowing the communication means to be bonded orsoldered to the circuit. This provides the advantage that the circuitcan be easily connected to the communication means of the data carrier,while at the same time an electrical contact with the sensor can beestablished, by having the sensor connection pads or wires eitherdirectly connected to the connection pads of the circuit or directlyconnected to parts of the communication means, which in all casesprovides an electrical connection between the sensor and the circuit viaonly the connection pads of the circuit to which the communication meansare connected.

Other solutions according to the invention offer the advantage that thesensor signal received via the connection pads of the circuit can bepicked up from the connection pads of the circuit in a well controlledand very efficient manner with or without being superimposed on the RFsignal for further processing.

Still other solutions of the invention offer the advantage that themeasurement time period for picking up or receiving the sensor signalcan be precisely defined or timed in dependence on e.g. furtherprocessing procedures, and consequently the timing can take otheroperations or operational modes of the circuit not related to theprocessing of sensor signals into account, thus avoiding any disturbanceof the other operations by the picking-up of the sensor signal.

Still other solutions of the invention offer the advantage that themeasurement time period will take physical boundary conditions intoaccount. These physical boundary conditions are either given byelectrical characteristics of the circuit (e.g. charging time constantof a measurement capacitor, power consumption of the circuit andavailable buffered power, or the like) and the electricalcharacteristics of the sensor or by the way the sensor signal isprocessed within the circuit. This will increase the reliability of theentire system.

Still other solutions of the invention offer the advantage that thesensor signal processing means offer a dedicated conversion of thesensor signal into a representation of the sensor signal which fits thefurther processing requirements. The sensor signal processing meansincorporating these dedicated sensor signal converting means renderpossible an independent operation (switch-on or -off) of the convertingmeans, independent of general processing means of the circuit. Thisrenders it possible to reduce the power consumption, because theconverting means only need to be in operation during a relatively shorttime period, which may or may not be equal to the measurement timeperiod.

Still other solutions of the invention offer the advantage that separategeneral processing means are provided which provide a dedicatedutilization of the representation of the sensor signal.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter, butthe invention is by no means limited to these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail by way ofnon-limiting example with reference to the embodiments shown in thedrawings.

FIG. 1 shows a data carrier according to a first embodiment of theinvention in the form of a block diagram.

FIG. 2 is a flow chart of a method according to the invention performedby the data carrier according to the first embodiment of the invention.

FIG. 3 is a block diagram of a data carrier according to a secondembodiment of the invention.

FIG. 4 is a block diagram a data carrier according to a third embodimentof the invention.

FIG. 5 is a flowchart of a method according to the invention performedby the data carrier according to the third embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a data carrier 1 designed for contactless communicationwith a so-called read/write station (not shown in FIG. 1) according tothe international standard ISO14443 Type A. It is noted that otherstandards, such as ISO 14443 Type B or other standards relating toso-called near-field communication (NFC) devices or to ultra highfrequency applications, may alternatively be used. Generic communicationprotocols may also be considered. In general, the combination of atleast one such a data carrier 1 and the read/write station realizes asystem for communicating data, as will be explained in more detailbelow.

The data carrier 1 comprises sensor means, a circuit 3, andcommunication means.

The sensor means are designed for providing a sensor signal SS thatrepresents an environment parameter. In the present case, the sensormeans are realized by a temperature sensor (denoted sensor 2 below) andthe sensor signal SS represents the ambient temperature adjacent thedata carrier 1. The sensor 2 comprises sensor connection pads 2A and 2Bdesigned to provide an electrical connection to the circuit 3. Thesensor 2 further comprises a radio frequency (RF) blocking inductance 4,a sensitive device 5, and a supporting energy source 6. As shown in FIG.1, the sensitive device 5 is connected in series with the RF blockinginductance 4, which ensures that an RF signal applied between the sensorconnection pads 2A and 2B is blocked from passing the sensitive device5. The sensitive device 5 is schematically connected to the supportingenergy source 6, such that the supporting voltage VDCS can be providedto the sensitive device 5 without disturbing the RF performance of thedata carrier 1. In the present case, the value of the sensor signal SSis a function of the ambient temperature. Obviously, however, othersensor types, e.g. gas identification sensors or air pressure sensors orradiation-sensitive sensors or the like, may also be used, and thesensor signal SS represents the respective environment parameter. It maybe further noted that the sensor signal SS may also show a form or shapeor a frequency or phase that is dependent on the environment parameter.

The communication means are realized as a dipole antenna CM. This dipoleantenna CM is designed for receiving an RF signal from the read/writestation and for providing said RF signal to the circuit 3 for thepurpose of supplying energy to the circuit 3 and for exchanging datawith the circuit 3. FIG. 1 shows only part of this dipole antenna CM.

The circuit 3 is realized as an integrated circuit. It is noted in thisconnection that a discrete realization is also possible. The circuit 3comprises first connection means designed for connection to thecommunication means CM of the data carrier 1. In the present case thefirst connection means are formed by connection pads 7 and 8, which areprovided and designed to allow the dipole antenna CM to be connected tothe circuit 3 by means of soldering. It is noted that the connectionmeans CM may be designed for establishing a bonding connection, i.e.designed as bonding pads, or alternatively designed as a plug-inconnector, but other techniques providing the required electricalconnection may also be considered.

The circuit 3 further comprises supply voltage generating means 9 andgeneral processing means 10 and sensor signal processing means 11A.

The supply voltage generating means 9 are designed for generating asupply voltage VDD based on the received RF signal and required forpowering the general processing unit 10 and at least parts of the sensorsignal processing means 11A. The supply voltage generating means 9comprise a Schottky diode 11B and a buffer capacitor 12 which areconnected in series between the connection pads 7 and 8, as shown inFIG. 1. The supply voltage generating means 9 further comprise ablocking capacitor 13, which provides a blocking of the DC supplyvoltage VDD, established by means of the Schottky diode 11B and thebuffer capacitor 12, from the dipole antenna CM in order to avoid anyshort-circuiting of the supply voltage VDD by the dipole antenna CM. Thesupply voltage generating means 9 further comprise a resistor 14connected in parallel with the buffer capacitor 12 for guaranteeing aminimum forward current for the Schottky diode 11B. Although theresistor 14 is described as an individual circuit element, it can bementioned that it basically reflects the load produced by the circuit 3that causes at least a minimum current flow.

The general processing means 10 are designed for processing data thatare transported by means of the RF signal from the read/write station tothe data carrier 1 and for communicating data back to the read/writestation by means of the RF signal. Several different designs forperforming these functions are known to those skilled in the art andwill therefore not be discussed in detail here. Focusing now on theinvention, the general processing means 10 are designed for generating atiming signal TS and providing it to the sensor signal processing means11A for allowing the sensor signal processing means 11A to process thesensor signal SS during a time period determined by the timing signalTS. The general processing means 10 are further designed to receive fromthe sensor signal processing mean 11A sensor data SD which represent thesensor signal SS, and to communicate these sensor data SD to theread/write station, e.g. upon receiving an inquiry command from theread/write station.

The sensor signal processing means 11A are designed for receiving saidsensor signal SS via said connection pads 8 and 7 and are designed forprocessing said received sensor signal SS in order to produce the sensordata SD. The sensor signal processing means 11 comprises a measurementcapacitor 15, a first switching transistor 16, a timing stage 17, and ananalog/digital converter 18.

The measurement capacitor 15 is connected between the connection pads 7and 8 in series with the first switching transistor 16, as shown inFIG. 1. The timing stage 17 comprises an input that is connected to thegeneral processing means 10 for receiving said timing signal TS. Thetiming stage 17 further comprises a first output that is connected tothe gate of the first switching transistor 16 for applying aconductivity control signal GS to the control electrode of the firstswitching transistor 16. In the present case, the first switchingtransistor 16 is a so-called enhancement mode Field Effect Transistor(FET) and therefore the control electrode is designated as “gate”. Inthe case of a bipolar transistor of e.g. the commonly known NPN or PNPtype, the control electrode is designated as “base”. The timing stage 17further comprises a second output that is connected to theanalog/digital converter 18 for applying a converter control signal CSto the analog/digital converter 18. The analog/digital converter 18 isconnected with its input between the measurement capacitor 15 and thefirst switching transistor 16 for sensing the analog value of thevoltage that can be tapped from the measurement capacitor 15 at thiscircuit point. Those skilled in the art will immediately understand thatthe measurement or data acquisition is performed on the basis of areference potential, which is not explicitly indicated in the Figures.It is further noted that a resistor, which would also enable a voltagedrop to be tapped, may replace the measurement capacitor 15.

In the present case, the timing signal TS triggers the timing stage 17to release the conductivity control signal GS for a certain measurementtime period t, such that during the measurement time period t the firstswitching transistor 16 is in its conducting mode and after themeasurement time period t the first switching transistor 16 is in itsnon-conducting mode. This causes the measurement capacitor 15 to becharged by the sensor signal SS during the measurement time period t.After the measurement time period t has elapsed, the timing stage 17releases the converter control signal CS, which triggers theanalog/digital converter 18 to convert the voltage picked up between themeasurement capacitor 15 and the first switching transistor 16 into thesensor data SD. The analog/digital converter 18 thus constituteconverter means designed for converting the sensor signal SS into arepresentation signal, i.e. representative of the sensor data SD.

Due to the fact that during the measurement time period t themeasurement capacitor 15 short-circuits the RF signal received via thedipole antenna CM and consequently the circuit needs to be powered bythe buffer capacitor 12, the measurement time period t is limitedbetween a lower time period limit t₁ and an upper time period limit t₀according to the following relation:t ₁ ≦t≦t ₀

The lower time period limit t₁ depends on the charging time constant forcharging the measurement capacitor 15, which is determined by thecapacitance value C1 of the measurement capacitor 15 and an ohmiccomponent RL2 of the RF blocking impedance L2 and a conducting moderesistance RT1 of the first switching transistor 16, as represented bythe following (first) equation:t ₁≧(RL2+RT1)·C1

The upper time period limit t₀ is defined by the electricalcharacteristics of the circuit 3. Of relevance is the power consumptionPCHIP at a minimum required supply voltage VDD value UCHIP and acapacitance value C₀ of the buffer capacitor 12. The following (second)equation shows the dependence of the upper time period limit t₀ on theseparameters:

$t_{0} \leq \frac{C_{0} \cdot {UCHIP}^{2}}{2 \cdot {PCHIP}}$

In order to guarantee a proper functioning of the data carrier 1, theparameters used in the two equations above, defining the two time periodlimits t₁ and t₀, need to be carefully weighed against each other.

In a further embodiment, a further RF blocking inductance can beconnected in series with the drain of the first switching transistor 16and a connection point CP to which the connection pad 7 and the blockingcapacitor 13 are connected. This further RF blocking inductance canimprove the operation of the circuit 3 because the RF signal ispractically blocked from being short-circuited by the measurementcapacitor 15 during the measurement time period t, and consequently theRF signal can still be used for generating the supply voltage VDD duringthe measurement time period t.

It is to be noted that the two signals CS and GS produced by the timingstage 17 may alternatively be produced by the general processing means10, in which case the timing stage 17 can be omitted. It may further benoted that the signal CS can be used to trigger the analog/digitalconverter 18 at the same moment at which the first switching transistor16 is switched to its conducting mode, which means that only one signalwould be required.

The operation of the data carrier 1 will be described below withreference to a flowchart shown in FIG. 2, which discloses a method ofinterrogating the sensor signal SS from the sensor 2 in the data carrier1, which is denoted method 19 in the following.

The method 19 starts in a block 20, where it is assumed that an RF fieldproduced by the read/write station is available at the location of thedata carrier 1.

The method 19 continues in a block 21, in which it is tested whether thereceived RF field produced by the read/write station is available at thelocation of the data carrier 1 with a sufficient strength in order tostart the operation of the data carrier 1, which is a basic requirement.If this basic requirement is not fulfilled, the method 19 branches backalong the N branch into a waiting loop until the basic requirement isfulfilled. If the basic requirement is fulfilled, the method 19 followsthe Y branch leading into a block 22.

In block 22, a standard operation of the data carrier is started, inwhich standard operation the data carrier will receive commands from theread/write station and communicate response messages back to theread/write station, the RF field being utilized for communicationpurposes and for powering the data carrier 1 in both cases.

According to the invention, it is also tested in a block 23 whethersensor data SD are desired. This desire may arise because of a commandreceived from the read/write station or because of an internal timing orlogic state or processing of software or firmware. If no sensor data SDare desired, the method 19 follows the N branch into the loop describedin the preceding paragraph. If sensor data SD are desired, the method 19follows the Y branch leading into a block 24.

In block 24, the first switching transistor 16 is switched into itsconductive mode and the method continues with block 25.

In block 25 it is checked whether the measurement time period t haselapsed. If the measurement time period t has not yet elapsed, themethod follows the N branch into a loop continuing testing whether themeasurement time period t has elapsed or not. In the meantime thecircuit 3 is powered by the buffer capacitor 12, and the sensor 2charges the measurement capacitor 15. If the measurement time period thas elapsed, the method follows the Y branch leading into a block 26.

In block 26, the first switching transistor 16 is switched into itsnon-conductive mode, which causes the charging of the measurementcapacitor 15 to be stopped and the circuit 3 to be powered by the RFfield. The method continues in a block 27, in which the analog/digitalconverter 18 is started for converting the analog voltage tapped fromthe measurement capacitor 15 into a digital representation given by thesensor data SD. After the analog/digital converter 18 has completed theconversion of the analog voltage into the sensor data SD, the sensordata are made available to the general processing means 10 for furtherprocessing, and the analog/digital converter 18 is switched off in orderto reduce the power consumption.

Depending on the actual application scheme defining how these sensordata SD are to be further processed, the sensor data SD are eitherinternally processed or communicated to the read/write station, orinternally processed whereupon a processing result is communicated tothe read/write station.

The procedure is then resumed at block 21.

In the present embodiment, the supporting energy source 6 is permanentlyconnected to the sensitive device 5, which significantly limits thelifetime of this energy source 6.

In contrast to the first embodiment, the second embodiment of theinvention provides a sensor 2 with extended lifetime of the supportingenergy source 6. The sensor 2 according to the second embodiment of theinvention comprises, in addition to the supporting energy supplyingsource 6 and the RF blocking inductance 4 and the sensitive device 5, aconnecting circuit 29 which is designed for connecting the supportingenergy source 6 to the sensitive device 5 only if an RF field isreceived. This provides that the sensitive device 5 is only powered whenthe circuit 3 is most likely to be active, which consequently provides asignificant probability of interrogating measurement signals SS from thesensor 2.

The connecting circuit 29 comprises a second switching transistor 30 ofthe enhancement mode FET type, which second switching transistor 30 isconnected between the supporting energy source 6 and the sensitivedevice 5, cf. FIG. 3, and comprises an RF detector circuit 31 connectedby its two inputs to the connection pads 7 and 8 and by its output to agate of the second switching transistor 30, as shown in FIG. 3. The RFdetecting circuit 31 comprises a second Schottky diode 32 and a secondbuffer capacitor 33, which are connected in series. The connection pointbetween the second Schottky diode 32 and the second buffer capacitor 33forms the output of the connecting circuit 29, to which the gate of theswitching transistor is connected. A second resistor 34 is connected inparallel to the second buffer capacitor 33. During operation, whichmeans that an RF field is available, the second Schottky diode 32 acts arectifier and rectifies the RF field, which charges the second buffercapacitor 33. The voltage built up at the gate of the second switchingtransistor 30 drives the second switching transistor 30 into itsconducting mode, such that the supporting voltage VDCS becomes availablefor powering the sensitive device 5. The second resistor guarantees aminimum current flow through the Schottky diode 32.

According to a third embodiment of the invention shown in FIG. 4, a datacarrier 1 is equipped with a sensor 2 of the passive type, which passivesensor 2, unlike the preceding embodiments, does not comprise thesupplying energy source 6. In the present case the circuit 3 comprisesmeasures that allow the operation of such a passive sensor 2.

In the present case the sensor signal processing means 11A comprise, inaddition to the first switching transistor 16, a first filter capacitor34, a second filter capacitor 35, and a third filter capacitor 36, whichthree filter capacitors 34, 35 and 36 realize RF signal damping means.It is noted that other filter means, such as active filters, may be usedinstead of the three capacitors 34, 35 and 36 or in addition to thesecapacitors 34, 35 and 36. The sensor signal processing means 11A furthercomprise a third resistor 37 and an amplifying stage 38. In the presentcase the amplifying stage 38 is designed as a non-inverting amplifierrealized by means of an operational amplifier. The amplifying stage 38is connected at its inverting input (−) to a connection point betweenthe first switching transistor 16 and the first filter capacitor 34. Thethird resistor 37 forms the feedback path of the amplifying stage.

Connected in parallel to the third resistor is the second filtercapacitor. Connected between the output of the amplifying stage 38 andthe first connection pad 7 is the third filter capacitor 36. Theamplifying stage 38 is connected at its non-inverting input (+) to thegeneral processing means 10. The amplifying stage 38 is furtherconnected to the timing stage 17 in order to receive an operationcontrol signal AT. The amplifying stage 38 is further designed to beswitched on or off in dependence on the operation control signal AT. Thepower supply voltage for the amplifying stage 38 is identical to thepower supply voltage VDD provided by the supply voltage generating means9 for the other parts of the circuit 3.

The timing stage 17 is designed to provide the conductivity controlsignal GS as discussed for the preceding embodiments. In addition, thetiming stage provides the operation control signal AT for the amplifyingstage 38 in a synchronous manner to the gate control signal GS.

In the present case, the general processing means 10 are designed toprovide a reference voltage V_(ref) for the amplifying stage 38.However, it is to be noted that a reference voltage source may also beprovided that is independent of the general processing means, e.g.forming part of the sensor signal processing means 11A. The generalprocessing means 10 are further designed to receive an output signalV_(out) of the amplifying stage 38 and to process this output signalV_(out) in order to determine the sensor data SD, which sensor date SDrepresent the sensor signal SS. The converter means are thus realized bythe amplifying stage 38 here, and the representation signal of thesensor signal SS is the output signal V_(out).

During operation the general processing means 10 trigger the sensor dataSD acquisition by releasing the timing signal TS to the timing stage 17.The timing stage 17 drives the first switching transistor 16 into itsconducting mode. During the following measurement time period t thecircuit is powered by the buffer capacitor 12 because the RF signal isdamped by the three filter capacitors 34, 35 and 36. The amplifyingstage 38 produces the output signal V_(out) according to the following(third) equation:

$U_{out} \cong \left( {1 + \frac{R_{2}}{R_{T}}} \right)$

where R₂ is the value of the third resistor and R_(T) is the, e.g.temperature-dependent, value of the sensing device 5. In the presentcase the resistance value R_(T) of the sensitive device 5 is computed bythe general processing means 10 according to the following (fourth)equation:

$R_{T} \cong {R_{2}\frac{U_{ref}}{\left( {U_{out} - U_{ref}} \right)}}$

and the physical value, e.g. the temperature, is retrieved by means of alookup table. In the present case the sensor data SD, which are furtherprocessed, do represent the temperature. However, it may be desired forsome reason to skip the computation of the resistance value R_(T) of thesensitive device. In this situation the output signal V_(out) isdirectly processed.

After having acquired the sensor date SD, the timing stage 17 drives thefirst switching transistor 16 back into its non-conductive mode andinhibits the operation of the amplifying stage 38. The operation of thedata carrier 1 then continues as known from the prior art, which allowsthe further internal processing of the sensor data SD or communicatingthe sensor data SD to the read/write station by utilizing the RF field.

Alternatively, the sensor data SD may represent the output signalV_(out) without prior conversion. In this situation the read/writestation has to process the so-called raw data further.

It may be mentioned that the three filter capacitors 34, 35 and 36 canbe omitted in a further embodiment. This implies that the RF field willbe present on the one hand for producing the supply voltage during themeasurement time period t, and on the other hand the RF signal will alsobe present in the output signal V_(out), which requires the generalprocessing stage 10 to perform more a sophisticated signal processing inorder to acquire the sensor data SD.

The operation of the data carrier 1 according to the third embodimentwill now be explained with reference to the method 19 according to theinvention as visualized in the flowchart of FIG. 5. In contrast to theflowchart of FIG. 2, the flowchart FIG. 3 shows new blocks 39 to 43following the block 23 known from the first embodiment.

In block 39, the first switching transistor 16 is driven into itsconductive mode, and the RF signal is damped by the RF signal dampingmeans. At the same time the amplifying means 38 are activated, whereuponthe method 19 continues with block 40.

In block 40, the general processing means 40 produce the referencevoltage V_(ref) and release it to the amplifying means 38, which intheir turn amplify the sensor signal SS according to the third equation,whereupon the method 19 continues with block 41.

In block 41, the general processing means 41 read the output voltageV_(out) from the amplifying means 38, whereupon the method 19 continueswith block 42.

In block 42, the general processing means 42 process the output signalV_(out) according to the fourth equation and derive the temperaturevalue from the lookup table, whereupon the method 19 continues withblock 43.

In block 43, the first switching transistor 16 is driven into itsnon-conducting mode and the amplifying means 38 are inhibited fromamplifying. The method 19 then returns to block 21.

To conclude, the measures as provided by the present invention providethe advantage that a relatively inexpensive conventional passive sensor2 or a conventional active sensor 2 or an improved active sensor 2according to the second embodiment of the invention can be used. Ineither case the sensor is simply connected to the connection means ofthe circuit 3 of the data carrier 1, to which connection means thecommunication means of the data carrier 1 are also connected.

It is noted that the general processing means 10 may be realized by aprocessor having a memory associated with it that is available withinthe circuit 3, or by a microprocessor having an internal memory.However, hard-wired logic circuits may also be considered.

Although the timing stage 17 was described above as a structural elementwithin the circuit 3, it is noted that it may alternatively be realizedby means of software executed by the general processing means 10.

It is to be noted that all embodiment of the circuit 3, in particularthe electronic components 11A, 9, and 10 of the circuit 3, will performin the same manner as described irrespective of whether they areconnected to the two connection pads 8 and 7 as shown in the first andsecond embodiment of the invention or as shown in the third embodimentof the invention. In fact, the circuit (3) provides a symmetry withregard to the electronic components 11A, 9, and 10 which enables it tobe connected to the pads 7, 8 in either way.

Although the Figures illustrating the various embodiments of theinvention show that the sensor means 2 are connected to parts of thecommunication means CM by means of the sensor connection pads 2A and 2B,and the communication means CM are finally connected to the connectionpads 7 and 8, it may be mentioned that the sensor connection pads 2A and2B may alternatively be directly connected to the connection pads 8 and7, e.g. on top of each other or side by side or in any other practicalmanner through well known measures.

Although the first switching transistor 16 is always shown as a fieldeffect transistor in the Figures and throughout the description of theseveral embodiments, it is noted that the function of the firstswitching transistor 16 may alternatively be realized by several othercomponents, e.g. analog switches, PNP transistors, and the like.

It may further be noted that the basic concept of designing the supplyvoltage generating means 9 can be replaced by any more advanced designknown to those skilled in the art, e.g. single or multiple voltage pumpsin combination with half- or full-wave rectifiers alone or incombination with linear voltage controllers.

It may further be noted that the basic concept of designing the RFdetection circuit 31 can be replaced by any more advanced design knownto those skilled in the art, e.g. single or multiple voltage pumps incombination with half- or full-wave rectifiers alone or in combinationwith linear voltage controllers.

Although dipole antennas are mentioned throughout the description, it isnoted that any other antenna, even so-called loop antennas forming adirect current short-circuit, or any other antenna not forming a directcurrent short circuit, e.g. so-called micro-patch antennas, or so-calledfolded dipole antennas, may also be considered.

It should be noted that the further processing of sensor data SD mayalso comprise storing of sensor data SD produced at differentmeasurement times (moments), such that a trend or a passing of athreshold can be judged.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.The word “comprising” does not exclude the presence of elements or stepsother than those listed in a claim. The word “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention may be implemented by means of hardware comprising severaldistinct elements, and/or by means of a suitably programmed processor.In the device claim enumerating several means, several of these meansmay be embodied by one and the same item of hardware. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measures cannot be used toadvantage.

1. A circuit for communicating an output signal representative of anenvironmental parameter, the circuit arrangement comprising: a firstconnection pad and a second connection pad arranged to receive a radiofrequency signal that communicates data and provides power to thecircuit arrangement, the first connection pad arranged to receive asensor signal that represents the environmental parameter, and the firstconnection pad and the second connection pad coupling the circuitarrangement for simultaneously receiving the radio frequency signal andthe sensor signal; a measurement circuit coupled to the first and secondconnection pads, the measurement circuit arranged to receive the sensorsignal via the first connection pad; a converter circuit coupled to themeasurement circuit and arranged to convert a signal output by themeasurement circuit into the output signal; and a shorting circuitcoupled to the measurement circuit and configured and arranged toshort-circuit the radio frequency signals between the connection padsduring a sensing period in which the measurement circuit measures thesensor signal.
 2. The circuit of claim 1, further comprising a voltagesupply circuit coupled to the connection pads, measurement circuit,converter circuit, and shorting circuit, the voltage supply circuitconfigured and arranged to power the circuit arrangement, and to storepower for powering the circuit arrangement while the radio frequencysignals are short-circuited.
 3. The circuit of claim 2, wherein thevoltage supply circuit includes a Schottky diode and a buffer capacitorcoupled in series between the connection pads.
 4. The circuit of claim1, further comprising a timing stage circuit coupled to the measurementcircuit, wherein: the measurement circuit includes a capacitor that isconnected to the first connection pad and a first switching transistorthat is connected in series with the capacitor and connected to thesecond connection pad; and the timing stage circuit is configured andarranged to provide a conductivity control signal to the first switchingtransistor for controlling a conductivity mode of the first switchingtransistor.
 5. The circuit of claim 4, wherein the timing stage circuitis further configured and arranged to generate and provide theconductivity control signal during a measurement time period t, suchthat the first switching transistor is driven into its conducting modeduring the measurement time period t.
 6. The circuit of claim 5, whereinthe timing stage circuit is further configured and arranged to providethe conductivity signal between a lower time period limit t₁, defined bya charging time constant of the capacitor, and an upper time periodlimit t0, defined by a power consumption determined by electricalcharacteristics of the circuit.
 7. A circuit for a data carrier, thedata carrier including a sensor circuit that is configured to provide asensor signal representative of an environment parameter and acommunication circuit that is configured to provide contactlesscommunication with an interrogator station, the circuit comprising: afirst connection pad and a second connection pad arranged to connect thecircuit to the communication circuit for communicating with theinterrogator station and for receiving radio frequency power from theinterrogator station, and arranged to connect the circuit to the sensorcircuit for receiving the sensor signal; a sensor signal processorincluding a measurement circuit coupled to the first and secondconnection pads, the measurement circuit arranged to receive the sensorsignal via the first connection pad, and the processor configured andarranged to process the received sensor signal, and in response to asignal from the measurement circuit provide an output to theinterrogator station via the first and second connection pads; whereinthe first connection pad and the second connection pad couple thecircuit for simultaneously communicating with both the communicationcircuit and the sensor circuit; and a shorting circuit coupled to themeasurement circuit and configured and arranged to short-circuit radiofrequency signals coupled to the connection pads from the communicationcircuit, during a sensing period in which the signal processor isreceiving a signal from the sensor circuit, via the respective pads. 8.The circuit of claim 7, wherein: the measurement circuit includes acapacitor that is connected to the first connection pad and a firstswitching transistor that is connected in series with the capacitor andconnected to the second connection pad, and the sensor signal processoris configured and arranged to provide a conductivity control signal to acontrol electrode of the first switching transistor for controlling aconductivity mode of the first switching transistor.
 9. The circuit ofclaim 8, wherein the sensor signal processor includes a timing stageconfigured and arranged generate and provide the conductivity controlsignal during a measurement time period t, such that the first switchingtransistor is driven into its conducting mode during the measurementtime period t.
 10. The circuit of claim 9, wherein the timing stage isconfigured and arranged to provide the conductivity signal between alower time period limit t₁, defined by a charging time constant of thecapacitor, and an upper time period limit t0, defined by a powerconsumption determined by electrical characteristics of the circuit. 11.A circuit arrangement for communicating an output signal representativeof an environmental parameter, the circuit arrangement comprising:means, including a first connection pad and a second connection pad, forreceiving a radio frequency signal that communicates data and providespower to the circuit arrangement, the first connection pad arranged toreceive a sensor signal that represents the environmental parameter, andthe first connection pad and the second connection pad coupling thecircuit arrangement for simultaneously receiving the radio frequencysignal and the sensor signal; means, including a measurement circuitcoupled to the first and second connection pads, for receiving thesensor signal via the first connection pad; means for converting asignal output by the measurement circuit into the output signal; and ashorting means, coupled to the measurement circuit, for short-circuitingthe radio frequency signals between the connection pads during a sensingperiod in which the measurement circuit measures the sensor signal. 12.A method for communicating an output signal representative of anenvironmental parameter, the method comprising: by using a firstconnection pad and a second connection pad, receiving a radio frequencysignal that communicates data and provides power to the circuitarrangement, the first connection pad arranged to receive a sensorsignal that represents the environmental parameter, and the firstconnection pad and the second connection pad coupling the circuitarrangement for simultaneously receiving the radio frequency signal andthe sensor signal; by using a measurement circuit coupled to the firstand second connection pads, receiving the sensor signal via the firstconnection pad; converting a signal output by the measurement circuitinto the output signal; and short-circuiting the radio frequency signalsbetween the connection pads during a sensing period in which themeasurement circuit measures the sensor signal.